1. Field of the Invention
The present invention relates to a data storage device having read/write heads for accessing information on a storage medium, and more specifically, to a mechanism for controlling the velocity of an actuator that moves the read/write heads in relation to the storage medium, particularly during head loading operations.
2. Description of the Prior Art
Data storage devices, and in particular, data storage devices of the type that accept a removable cartridge containing a disk-shaped storage medium, usually employ either a linear actuator mechanism or a rotary arm actuator mechanism for positioning the read/write head(s) of the disk drive over successive tracks of the disk-shaped storage medium. In most disk drives, and particularly in those that receive removable disk cartridges, the linear or rotary arm actuators are moved to a retracted, or parked position when the disk drive is not in use. In such a retracted position, the read/write heads of the disk drive are moved off and away from the surface(s) of the storage medium in order to prevent damage to the head(s) and storage medium. In order to resume use of the disk drive, the read/write heads must once again be loaded onto the surface(s) of the storage medium so that the data transfer can begin. It is important that the head loading operation be carried out in a controlled manner to prevent damage to the read/write heads.
Couse et al., U.S. Pat. No. 4,864,437, describe a head loading velocity control mechanism for a disk drive that measures the back EMF voltage across the actuator of the disk drive to obtain an indication of the velocity of the actuator. The measured back EMF voltage is then employed in a control scheme to control the velocity of the actuator during a head loading operation. Unfortunately, the circuitry needed to measure the back EMF voltage across the actuator increases the cost and complexity of the disk drive. Furthermore, this technique provides only a rough control of the actuator velocity, which may not be acceptable in many applications.
Lee, U.S. Pat. No. 5,128,813, describes a velocity control technique for a disk drive actuator that employs thermal measurements to estimate the velocity of the actuator. Again, however, the circuitry necessary to obtain accurate thermal measurements unduly increases the cost of the disk drive, and this technique is susceptible to inaccuracies.
Other prior art devices employ high-precision glass scales affixed to a disk drive actuator for obtaining accurate position and track counting information during track seek operations. See, e.g., Thanos et al., U.S. Pat. No. 5,084,791. Unfortunately, the cost and complexity of the high-precision glass scales and associated optical circuitry make them disadvantageous.
Certain products in the "BETA" line of Bernoulli disk drives manufactured by Iomega Corporation, the assignee of the present invention, employ an optical sensor and a gray-scale pattern affixed to a linear drive actuator to obtain an indication of the linear position of the actuator. However, these products do not, and are not capable of, deriving or controlling the velocity of the actuator using the position information generated with the gray-scale pattern and optical sensor.
As the foregoing illustrates, there is a need for a simple, cost efficient mechanism for controlling the velocity of a disk drive actuator, particularly during head loading operations. The present invention satisfies this need.